1. Field of the Invention
The present invention relates to a breather structure for a final reduction gear equipped with a differential. In particular, the invention is addressed to a breather structure of reduced cost, reduced noise and durability, and which prevents oil leakage.
2. Background Art
A conventional gear box exists for storing a gear, a bearing, and lubricant. In the conventional gear box, a communication pipe-like breather structure prevents changes in internal pressure due to increasing temperature, so that the internal pressure is always made equivalent to the atmospheric pressure. This prevents oil leakage from a sealed part due to increasing internal pressure.
Such a system is disclosed in Japanese Utility Publication No. Sho. 57-51940 entitled xe2x80x9cFinal Reduction Gear.xe2x80x9d In FIG. 4 of this publication, a final reduction gear includes an air introducing slot 9A of an air breather 9 in a space surrounded by ribs 8, 8A on the inside of the rear cover 5. A shroud 10 is located on the rear cover 5 to prevent oil scattered by a rotating hypoid gear from entering the air introducing slot 9A and the upper surface of the rib 8A.
In FIG. 5 of the publication, another embodiment of a final reduction gear includes a packing 6, provided between the housing 4 and the rear cover 5. The packing 6 is formed as partly projecting so that oil is prevented from entering the air introducing slot 9A and the upper surface of the rib 8A.
According to the above technique, attachment of a shroud 10 to the rear cover 5 results in an increased number of parts. The parts include the shroud 10, a bolt for attachment, and so on. The increase in number of parts increases costs.
Also, when the packing 6 is formed as partly projecting, a thin packing that is less rigid is likely to vibrate, which results in increased noise and decreased durability.
Further, as the hypoid gear 1 rotates at a high speed, the amount of scattered oil increases and its velocity increases. Therefore, a larger amount of oil may enter the air introducing slot 9A or the upper surface of the rib 8A, through spaces between the rib 8A and the shroud 10, or between the rib 8A and the extension of the packing 6.
In view of the above, objects of the present invention include providing a breather structure for a final reduction gear having a decreased cost, less noise, increased durability, and which may prevent oil leakage.
In order to achieve the above objects, a final reduction gear, in which an upper part of a housing is made into a breather chamber, which is communicated to the outside via a breather pipe, and a differential is rotatably stored in a housing. A plurality of oil stop ribs are provided, extending toward the differential, on an inner circumferential surface of the housing, to prevent oil having been scooped by the differential from flowing into the breather chamber. The oil stop ribs may be provided at irregular intervals.
When the scooped oil is prevented from flowing into the breather chamber by the plurality of oil stop ribs formed on the inner circumferential surface of the housing, and the adjacent oil stop ribs are provided at irregular intervals, a place where the oil is to be accumulated is shifted from a place between adjacent oil stop ribs with a larger interval to a place between adjacent oil stop ribs with a smaller interval as the differential rotates at a higher rotation frequency. In this manner, an amount of oil to be blocked is gradually reduced.
As oil stop ribs are provided to the housing, the need to provide additional oil stopping parts to the housing is eliminated. This reduces the number of parts and suppresses noise or damage due to vibration.
Also, when adjacent oil stop ribs are provided at irregular intervals, an amount of oil to be blocked can be gradually reduced as the differential rotates at a higher rotation frequency, whereby the oil can be reliably prevented from flowing into the breather chamber.
The oil stopping ribs may be formed having upper and lower surfaces of differing shape. Specifically, the upper surface of the oil stop rib may be formed as declining, and may have a curvature, so that the blocked oil flows downward, and the lower surface thereof is formed as a receiver for directly receiving the rising oil.
The blocked oil flows downward along the declining upper surface of the oil stop rib, while the rising oil is received by the lower surface of the oil stop rib, which is formed as a receiving surface.
As a result, oil does not accumulate on the upper surface of the oil stop rib, and oil flow is blocked by the lower surface of the oil stop rib, so that the oil can accumulate in the lower part of the housing.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.